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Should the camera look right at the corner of calib. panels?

The place for questions, problems, comments and tips regarding the camera calibration.

Should the camera look right at the corner of calib. panels?

Postby Lunat1c » Wed Aug 07, 2013 3:51 pm

Should the camera look right at the corner of calibration panels so that the 2 panels occupy the same amount of space on the screen? If I try to make this, then there is very less room left for projector to look at the panels. So it becoes that, one side of the panels has sharp patterns, while the other side has faded patterns. Does this affect the quality? Or is it not so important for the camera to look right at the center of the corner?
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Re: Should the camera look right at the corner of calib. pan

Postby Sven » Wed Aug 14, 2013 9:24 am

The camera does not have to look precisely at the center. Neither does the projector.
It is more important that
- both look at the same region (camera sees nearly the whole projection, and not much more around it)
- The whole camera image is filled with calibration markers (not all markers must be visible)

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Re: Should the camera look right at the corner of calib. pan

Postby Lunat1c » Wed Aug 14, 2013 3:25 pm

Hi Sven, thnx for the reply.

As you say, focusing is important. There is one more issue I'm confused about. According to the manual, first I put the object in front of the scanner and make adjustments. Then it says "Remove the object and set up the calibration corner in the same area in front of the scanner."
How "in the same area",

My object is on the center of the turntable. Should the corner of the calibration panel be put right at the point where there was the center of the turntable (hence the object)? Does that need to be precise?
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Re: Should the camera look right at the corner of calib. pan

Postby Sven » Wed Aug 14, 2013 3:55 pm

Probably the center of the calibration panel will be placed a little further away than the object.
The rule is: Without changing anything at the scanner, place the calibration corner so that
- The projection is well focused (at average distance)
- The projection is not larger than the calibration pattern
- The camera can see more or less the same region which the projector illuminates (as much as possible)
- The camera can see a good part of the calibration pattern (at least the 6 ring markers)

With these conditions, you will calibrate the scanner in the same region where you will scan (relative to the scanner). That's ideal.

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Re: Should the camera look right at the corner of calib. pan

Postby KNSCI » Wed Mar 19, 2014 1:05 pm

This thread helps me clarify some confusion about the Wiki/GSG instructions, thanks.
I have the big calibration panels and right-angle brackets. With projector and camera and object set up and focused, I remove the object and put the panels in but then the projector doesn't illuminate the right calibration pattern for the size of object. So I've tilted the red bar without touching projector or camera focus until the projector illuminates six circles and as many dots as possible, and moved the calibration panels closer and further to/from the projector until it's focused, not in the corner crevice, but about midway out each panel.
Since the camera lens on its ball mount is higher than the projector lens, it looks down so doesn't see all of the projection.
I'm trying to keep the panels solidly on the table instead of tilting them by hand to accommodate the angle of the camera.
Am I doing it right or wrong?
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Re: Should the camera look right at the corner of calib. pan

Postby Sven » Fri Mar 21, 2014 6:56 pm

Sounds like you're doing it right. :D

Since the camera lens on its ball mount is higher than the projector lens, it looks down so doesn't see all of the projection.
By moving the calibration panel or the whole scanner, you should be able to make the camera see the projection. (It need not be 100% the same.)

I'm trying to keep the panels solidly on the table instead of tilting them by hand to accommodate the angle of the camera.
I'm not sure what you mean. The camera looks from a different direction than the projector (from further left/right and from further above), that is necessary for scanning and not a problem. The camera may look at the calibration panels from "any" angle, just not too flat, so that it can see the markers clearly.

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Re: Should the camera look right at the corner of calib. pan

Postby KNSCI » Sat Mar 22, 2014 7:17 am

Thanks, Sven your reply helps for sure.
Tilting by hand I meant, with the scanner assembly focused for the object, I put the panels in place of the object, so that it sits by itself. If the camera doesn't see the dots and circles, I can tilt the panels by hand so projection covers more dots and circles, and the camera sees enough, but that's not a very solid arrangement for the duration of camera calibration.
I think if I either raise the object so the panels fall in line of projection, or go ahead and tilt the assembly, both as discussed in other threads, I should be ok.
Thanks for thoroughly scouring these forums and being so good about responding. I really need to get up to speed soon to fulfill some promises and you're helping me get more confidence that I'm getting the most out of the kit that I can.
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